The present invention is directed generally to a protractor and, more specifically, to a protractor for use by draftsmen and machinists.
Protractors are made for a variety of purposes. Some are designed specifically for draftsmen and others for machinists and mechanics. A draftsmen's protractor includes a generally semi-circular base having a straight edge and a 180.degree. scale. A measuring arm is pivotally mounted on the base for measuring the angle of a line relative to the straight edge of the base. This type of protractor is capable of measuring all angles between 0.degree. and 360.degree. on a planar surface. However, the draftsmen's protractor is not acceptable for use by a machinist or mechanic. It is awkward to use on machine surfaces; also, it is capable of measuring only certain angles between adjacent machine surfaces and cannot be used to measure inside angles.
The conventional machinists protractor includes a base having two right angle edges and a 90.degree. arcuate scale of markings. A measuring element is pivotally mounted on the base and has a measuring arm that cooperates with one of the straight edges of the base and an indicator arm integrally formed with the measuring arm provided with a measuring mark adapted to coincide with the marks on the arcuate scale. One straight edge of the base is placed along one surface and the measuring element is swung so that a straight edge of the measuring arm lies along an adjacent surface. The angle between the two surfaces is determined by viewing the position on the scale of the mark on the indicator arm. The protractor is capable of measuring inside angles between 90.degree. and 180.degree.. However, there are many outside angles that cannot be measured. Various machinists protractors have been developed to overcome this deficiency of machinists protractors. Such protractors include additional indicator and measuring arms resulting in a complicated and expensive protractor. In addition, the specialized machinists protractors are unacceptable for use by draftsmen. These and other difficulties experienced with the prior art devices have been obviated in a novel manner by the present invention.
It is, therefore, an outstanding object of the invention to provide a protractor which can be used by both machinists and draftsmen.
Another object of the invention is the provision of a protractor that is capable of measuring all angles on a planar surface and most inside and outside angles between adjacent machine surfaces.
A further object of the present invention is the provision of a protractor having a single measuring arm and a single indicator arm that has the measuring range of protractors employing multiple indicators and measuring arms.
It is another object of the instant invention to provide a protractor in which the indicator arm is adjustable relative to the measuring arm to increase the measuring range of the protractor.
A still further object of the invention is the provision of a protractor which is simple in construction and which is easy to use.
It is a further object of the invention to provide a protractor which is inexpensive to manufacture and which is capable of a long life of useful service with a minimum of maintenance.
With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.